CHAPTER 3 NOTES-Mendel was analyzing descendants of pure lines that differed in tow characters. -Dyhybrid- a double heterozygote such as A/a * B/b-Dihybrid crosses - A cross between two individuals identically heterozygous at two loci—for example, A B/a b× A B/a b.-Mendel’s Second Law - different gene pairs assort independently in gamete formationoFor two heterozygous gene pairs A/a and B/b, the “b” allele is just as likely to end up with an “A” allele. Law applies to genes in diff. chromosomes. o2 alleles for a gene are packed into separate gametesoAlleles get back together after fertilization.-Law of independent assortment - genes on different chromosomes are transmitted independently of one another. -Mendellian Ratios describe that equal segregation and independent assortment are fundamental hereditary processes found throughout nature. oRatios: 3:1:1:1, 9:3:3:1 and 1:1:1:1-Independent assortment on haploidsoFusion of parental cells result in transient diploid - meiocyte that is a dihybrid A/a; B/b and the randomly sampled products of meiosis. 3.2.1Geneticist can work in either of two directions:(1) predicting the genotypes of parents by using ratios of progeny or (2) predicting progeny ratios from parents of known genotype.Methods of independent assortment:(A) Punnett squares can be used to show hereditary patterns based on one gene pair, two gene pairs, or more.-as long as 2 non-allelic genes are on diff. chromosomes:oThey will assort independentlyoCan FOIL to find gametes (combine first, outers, inners, lasts).(B) The branch diagram is easier to create and is adaptable for phenotypic, genotypic, or gametic proportions. -Used for independent assorting, non-allelic genes only (genes on diff. chromosomes).

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-Useful for dihybrids and upoEx AaBbCC X AabbCC what is the probability will have baby AabbCC. ASK TEACHER !!-Use dash notation if looking for phenotypic rations only; A- means AA or Aa.(C) To simplify, we can use a statistical approach, which constitutes a third method for calculating the probabilities (expected frequencies) of specific phenotypes or genotypes coming from a cross: (1)Product Rule- The probability of two independent events occurring simultaneously is the product of the individual probabilities.- The focus is on outcomes A and B(2)Sum Rule- The probability that one or the other of two mutually exclusive events will occur is the sum of their individual probabilities.- The focus is on the outcome A′or A″.*** IF question asks how many progeny do we need to grow? First calculate the proportion of progeny expected to be of that genotype. Book example=256. approach by probability of complete failure where 1-1/256)=255/256 extending idea to sample size “n” = (255/256)n. The probability of obtaining once success is 1 minus the probability of total failure 1-(255/256)n = .95 or 95%.

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